-
Democritus's Atomic Theory (375 B.C.E.)
Democritus was an ancient philosopher who was the first to come up with the idea of atoms. He theorized that everything was made of atoms, and he got the name from the greek word "Atomos," meaning indivisible. -
Lavoisier's Priniple of Mass Conservation
This principle states that within any system where matter and energy cannot escape, the mass of the whole system must remain the same over time. This is because mass can be neither created or destroyed, only rearranged or transformed. -
Dalton's Spherical Model
This model of the atom, by John Dalton, took the ideas of Democritus and turned them into a substantive item, i.e. something which could be seen and referenced rather than just imagined. -
Proust's Law of Definite Proportions
Proust found that "a chemical compound always contains exactly the same proportion of elements by mass." This means that in every instance of a substance (for instance, water) there will be the same distribution of elements (twice as much Hydrogen as Oxygen, given by H2O). -
Thomson's Cathode Ray
Thomson fired rays from a Cathode to an Anode, and applied different electrical currents to see how the rays were displaced. He used a ratio of how strong the current was to how much the ray was displaced, and found that the particles either carried a huge charge or were thousands of times smaller than Hyrdogen-1. He decided on the latter and proposed that cathode rays were made of particles from within atoms themselves, thus discovering electrons. -
Thomson's Plum Pudding Model
Thomson's theory was that the atom was made up of negatively charged electrons (which he called corpuscles) which floated around in a positively charged cloud. He named this model after a popular dessert at the time, Plum Pudding. -
Rutherford's Gold Foil Experiment
Rutherford perfomed this experiment where he shot alpha particles at a thin piece of gold foil, and recorded where they ended up on a screen surrounding the foil. Most alpha particles passed right through, as expecterd, however very, very rarely some would bounce in odd directions. -
Rutherford Discovers the Nucleus
From the results of his Gold Foil Experiment, Rutherford concluded that the particles must be coming into contact with something dense that deflects them. He determined that it was a positively charged mass in the center of the atom. -
Rutherford's Nuclear Model
From his recent findings, Rutherford developed a new model of the atom. His model states that an atom is made up of a central positive charge (which we now call the nucleus, but Rutherford himself did not) surrounded by a cloud of orbiting electrons. -
Bohr 's Bohr Model
Working in the same lab as Rutherford, Bohr quickly noticed a hole in the scientist's new theory. This problem was that if electrons were in a true orbit, they would spin into the nucleus in a fraction of a second.So he did research which led him to the Bohr Model, which stated that electrons could only follow certain paths of orbit called energy levels, and that they could switch between them, but in switching never occupied the space between. -
Rutherford Discovers the Proton
Rutherford actually found that the nucleus of Hydrogen-1 was found in all other nuclei. Because we now know the nucleus of a Hydrogen-1 atom consists of only a single proton, this discovery is credited as the first proton found. -
Schrödinger's Quantum Mechanical Model
Schrödinger saw that the dispute between the school of old scientific thinking and the school of new scientific thinking was going nowhere, and as such it hit him that the answer was, in fact, a compromise. He found that the electrons in an atom do orbit in energy levels as Bohr thought, however it is not a circular orbit. Rather, there was a chance of finding an electron anywhere outside the nucleus, and this chance was given by Schrödinger's own wave equation. -
Heisenberg's Matrix Mechanics
Matrix Mechanics are the first actually consistent attempt at what we now know as Quantum Mechanics. They also began a new branch of science known as Quantum Theory. They built on the Bohr model, attempting to explain how a "quantum jump" (the term for when an electron switches orbits without touching the space in-between) can occur. It claimed that particles were a bunch of matrices which evolved over time. -
Heisenberg's Uncertainty Principle
This principle states that an electron's position and velocity cannot simultaneously be known, with legitimate accuracy. This is due to a jolt-like reaction the particle has from the mere act of being observed. -
Bothe's and Becker's Strange Gamma Rays
Bothe's and Becker's work stated that shooting beryllium with radioactive alpha particles made radiation which penetrated but didn't effect the charge. Most scientists at the time assumed this was a strange variation of gamma ray. -
Chadwick Discovers the Neutron
Chadwick didn't believe that Bothe and Becker had indeed just found gamma ray, so he disproved that theory by performing the experiments again, but shooting different elements. The findings were so inconsistent with any suggested concept that Chadwick concluded it must be a different particle within an atom, one without charge. -
Chadwick's Modified Nuclear Model
Chadwick's discovery of the neutron led him to create a new atomic model which includes it. He correctly stated that the neutron lies in the nucleus along with the protons. -
Zweig and Gell-Mann's Quarks
Zweig and Gell-Mann actually worked independently, but both found that there are things smaller than electrons, which may be what make up protons and neutrons. These things, called "quarks," are proposed to be truly elementary particles, which means that nothing is smaller than them. They are the "building blocks" from which all atomic particles are made.
